Mobile machines, such as on-highway or off-highway vehicles, excavating machines, aircrafts, marine vessels, and locomotives, as well as stationary machines, such as engines, generators, motors, and electronic appliances, typically generate a substantial amount of heat during operation. The heat, if not properly managed, can reduce fuel efficiency and/or cause premature wear or damage to machine components. As such, machines typically implement cooling systems to divert the heat away from the machine during operation. These cooling systems may include, among other things, a cooling fan configured to draw heat away from and/or push cooler airflow toward machine components.
Due to varying environmental conditions, cooling fans are often operated at variable speeds to provide variable cooling rates. For example, an off-highway truck hauling a heavy load up a steep incline in high ambient temperatures may require a higher rate of cooling than if the truck were stationary and idling with little to no load under cooler conditions. To the extent it may be necessary and/or efficient to run the cooling fan at a high speed under the former instance, it may be unnecessary and inefficient to run the fan at the same high speed under the latter instance. Although many conventional cooling systems provide some form of variable fan speed control for different conditions, there are still some conditions that are overlooked and not appropriately accounted for.
One such condition involves transmission calibrations. The transmission of a machine typically includes hydraulic clutches that are used to shift between different input/output gear ratios within the transmission. Such transmissions also often include two input shafts and one output shaft, as well as one or more trains of interrelated gear elements that selectively couple the input shafts to the output shaft. Shifting from one gear ratio to another normally involves releasing or disengaging off-going clutches associated with the current gear ratio and applying or engaging oncoming clutches associated with the desired gear ratio. Furthermore, each clutch may be controlled via electrically controlled solenoid valves which control the fluid pressure to the clutch and hence the clutch movement.
The clutches within a transmission are generally controlled with respect to the engagement force of individual clutches, as well as the phase between clutch activations, or the phase between releasing an off-going clutch and activating an oncoming clutch. The force and phase with which the transmission clutches are manipulated greatly impact the resulting shift quality. For example, if an off-going clutch disengages prematurely, the engine speed may surge momentarily before torque is transferred, which can cause an abrasive shift and accelerated wear on machine components. Alternatively, an oncoming clutch which engages prematurely can cause a suboptimal shift and accelerated wear on the clutch or other machine components. The force and phase of each clutch are therefore occasionally calibrated in order to maintain efficiency and service life of the machine and the transmission.
In comparison to normal operating conditions, a typical calibration routine operates the transmission and the overall machine at low or negligible load levels. Correspondingly, the machine generates much less heat during a transmission calibration than it would otherwise generate under normal loads during normal machine operations. However, being unable to distinguish between normal machine operations and a calibration routine, conventional cooling schemes will proceed to cool the machine at relatively higher cooling rates according to normal operating standards despite the low cooling demand of transmission calibrations. As a result, transmission fluids are often overcooled to temperatures that are below the acceptable range, and the transmission cannot be properly calibrated accurately or efficiently.
Some conventional cooling systems offer variable cooling rates to adjust for special circumstances which may occur during operation of a machine. For example, U.S. Pat. No. 8,714,116 (“Hartman”), discloses a fan speed control system which lowers fan speed to minimize speed differentials between a fan and a fan drive. The system in Hartman, however, does not protect against overcooling conditions and does not modify fan speeds in response to a transmission calibrations or other low load and low temperature operations. Moreover, Hartman does not provide overriding cooling schemes that can be selectively enabled or disabled based on the various operating conditions of the machine and/or the transmission.
In view of the foregoing inefficiencies and disadvantages associated with conventional cooling systems, a need exists for more intuitive thermal management systems and methods which protect against not only overheating conditions, but also overcooling conditions. Moreover, a need exists for thermal management systems and methods which can override conventional or default cooling schemes during low load and low temperature operations which are susceptible to overcooling.